The present invention relates to power tongs used to apply torque to tubular members in the oil exploration/production industry. In particular, the present invention deals with a novel device for converting a pivoting jaw power tong into a sliding jaw power tong.
Both pivoting jaw and sliding jaw power tongs are well known in the art. An example of a pivoting jaw power tong can be seen in U.S. Pat. No. 4,350,062 to Farr et al, which is incorporated by reference herein. FIG. 1 illustrates the basic components of a pivoting jaw power tong 1. A tong body 2 will enclose a ring gear 3 which will have a cam surface 4. Positioned within ring gear 3 are the pivoting jaws 5. Pivoting jaws 5 are pivotally attached between an upper and lower tong cage plate (not shown) by pivot pin 7. A roller 6 on pivoting jaws 5 will engage cam surface 4 on ring gear 3. As is well known in the art, the rotation of ring gear 3 will cause different sections of cam surface 4 to either push roller 6 toward tubular 100 (and thus cause the jaws to grip the tubular) or allow roller 6 to move away from tubular 100 (causing the jaws to release the tubular).
An example of a sliding jaw power tong may be seen in U.S. Pat. No. 5,435,213 to Buck which is incorporated by reference herein. A sliding jaw power tong has a tong body and ring gear structure similar to a pivoting jaw power tong, but the jaw is not pinned to the cage plates. A pocket for housing the sliding jaw is formed in the cage plates and the sliding jaw is moved radially toward the tubular by way of the ring gear""s cam surfaces acting on the sliding jaws"" rollers.
One advantage which pivoting jaw power tongs have relative to the sliding jaw variety is that pivoting jaw power tongs have a somewhat smaller overall diameter. This smaller diameter is a result of pivoting type jaws needing less radial distance within the ring gear to open and receive a tubular than is the case with sliding jaw power tongs. However, pivoting jaws also have certain disadvantages compared to sliding jaws. Generally both pivoting jaw and sliding jaw power tongs are designed to grip a range of standard tubular diameters with varying jaw sizes designed for each standard tubular diameter. For example, a 14xe2x80x3 power tong will typically accommodate different jaw sizes for the gripping of 14xe2x80x3 diameter down to 5xe2x80x3 diameter tubulars. Nevertheless, because of the pivoting geometry of the pivoting jaw power tongs, these power tongs tend to grip out of tolerance tubulars with a less uniform load than sliding jaw power tongs, thereby causing damaging slippage between the jaws and the tubular. For certain types of tubulars such as well casing and production tubing, this is not a significant problem because these tubulars generally manufactured and maintained within relatively tight tolerances (e.g. +/xe2x88x92{fraction (1/32)}xe2x80x3). However, with other tubulars such as drill pipe, the tool joint of the tubular can vary significantly in diameter (e.g. xc2xcxe2x80x3) and such relatively large variations in diameter can cause a tubular to not be reliably gripped by pivoting jaw tongs.
Because sliding jaws move on a straight radial path toward and away from the tubular, this type of power tong can grip the tubular with an equally uniformly applied load over a wider range of radial distances. Thus, the wider variance in diameters found in drill pipe does not adversely effect the gripping ability of sliding jaw power tongs.
Additionally, there will be occasions in tubular handling operations when only a pivoting jaw tong is available and large tolerance tubulars must be manipulated with that power tong. It would be a significant advantage if there was a quick and economical manner of converting a pivoting jaw power tong into a sliding jaw power tong.
The present invention provides a jaw adapter for use in a pivoting jaw power tong having a cage plate designed to house a pivoting jaw member. The jaw adapter includes an adapter body shaped to fit between the cages plates of the pivoting jaw power tong. The adapter body further includes a pin assembly for engaging at least one of the cage plates, and the adapter body still further includes a sliding jaw passage. A jaw assembly is positioned within the sliding jaw passage.
The present invention also includes a method of converting a pivoting jaw power tong into a sliding jaw power tong. The method comprises the steps of: a) providing a pivoting jaw power tong; b) removing the pivoting jaw from the power tong; and c) positioning a sliding jaw adapter within the power tong. The sliding jaw adapter includes an adapter body shaped to fit between the cages plates of the pivoting jaw power tong. The adapter body further includes a pin assembly for engaging at least one of the cage plates, and the adapter body still further includes a sliding jaw passage. A jaw assembly is then positioned within the sliding jaw passage.